Generating Magnetic Field Map for Indoor Positioning

1. An apparatus, comprising: at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to: acquire information indicating a measured magnetic field vector and information relating to an uncertainty measure of the measured magnetic field vector in at least one known location inside a building, wherein the indicated magnetic field vector represents magnitude and direction of the earth's magnetic field affected by the local structures of the building, and wherein the known location is defined in a frame of reference of a floor plan of the building, and the uncertainty measure represents at least one of uncertainty of the magnitude of the magnetic field vector and uncertainty of the direction of the magnetic field vector and indicates location-specific reliability of the measured magnetic field vector in the at least one known location; generate an indoor magnetic field map for at least part of the building on the basis of at least the acquired information and the floor plan, wherein the indoor magnetic field map comprises the magnetic field vector and the uncertainty measure of the magnetic field vector for the at least one location inside the building; and apply the uncertainty measure of the magnetic field vector comprised in the indoor magnetic field map for at least one of the following: location estimation of a person in the building ( 100 ), updating the generated indoor magnetic field map with new magnetic field vector measurements.

2. The apparatus of claim 1 , wherein the uncertainty measure of the magnetic field vector is location specific and is determined on the basis of at least one of the following: number of at least one existing magnetic field vector measurement in the location, physical distance to the at least one existing magnetic field vector measurement from the location, amount of deviation between at least two different magnetic field vector measurements for the location, amount of variance in local motion data provided by one or more inertial sensors coupled to a measuring device that measured the magnetic field vector in the location, a specific model and/or type of the measuring device, an electrical state of the measuring device, geolocation of the measuring device, time stamp of the at least one existing magnetic field vector measurement in the location.

3. The apparatus of claim 1 , wherein the apparatus is further caused to: acquire information indicating a three-dimensional orientation of a measuring device at the at least one time instant when the magnetic field vector is measured, wherein the acquired magnetic field vector is measured by the measuring device and defined in a frame of reference of the measuring device; and adjust the acquired magnetic field vector from the frame of reference of the measuring device to the frame of reference of the floor plan on the basis of the acquired information indicating the three-dimensional orientation of the measuring device.

4. The apparatus of claim 1 , wherein the apparatus is further caused to: acquire information indicating a virtual measurement path along which a measuring device measured the magnetic field vector, wherein the virtual measurement path is defined in the frame of reference of the floor plan; determine a tangent vector of the indicated virtual measurement path in the direction of movement of the measuring device; and apply the determined tangent vector in determining what the rotation about the vertical axis of the measuring device is at any given point along the virtual measurement path.

5. The apparatus of claim 1 , wherein the apparatus is further caused to: acquire the information indicating the magnetic field vector from a measuring device that has measured the magnetic field vector; and provide, on request, at least part of the generated indoor magnetic field map to a positioning device that is to determine its location inside the building.

6. The apparatus of claim 5 , wherein the part of the generated indoor magnetic field map to provide is selected on the basis of location estimate of the positioning device, wherein the location estimate is acquired from a non-magnetic field based location discovery system.

7. The apparatus of claim 5 , wherein the apparatus is further caused to: provide at least one candidate virtual measurement path or area to the measuring device along or in at least one of which the measuring device is suggested to measure the magnetic field vector, wherein the selection of the at least one candidate virtual measurement path or area is based at least partly on the location specific uncertainty of the magnetic field vector.

8. The apparatus of claim 5 , wherein the apparatus is further caused to: acquire at least one image or image feature of the surroundings of the location in the building where the magnetic field vector is measured from the measuring device, wherein the at least one image depicts at least one of the following: a floor, a ceiling, at least one wall, and the at least one image is captured when the measuring device has a predetermined three-dimensional orientation; and provide, on request, the at least one image or image feature to the positioning device who is to determine its location inside the building, wherein the at least one image is usable in location discovery of the positioning device in the building.

9. The apparatus of claim 5 , wherein the apparatus is further caused to: acquire information indicating the magnetic field vector in at least one known location inside the building from at least two different measuring devices; and combine the acquired information to represent the magnetic field vector and the uncertainty measure of the magnetic field vector.

10. The apparatus of claim 5 , wherein the apparatus is further caused to: determining whether a certain acquired magnetic field vector is valid or not on the basis of at least one of the following: at least one acquired image or image feature of the surroundings of the location where the certain magnetic field vector is measured, statistical properties of the certain magnetic field vector measured, amount of variance in local motion data provided by one or more inertial sensors coupled to the measuring device, a difference between the expected direction of the magnetic field vector and the measured direction of the certain magnetic field vector, a determined average speed during the measurement of the certain magnetic field vector, an estimated rank of the user associated with the measuring device that measured the certain magnetic field vector; and decide either to remove the certain magnetic field vector from the acquired information or to utilize the certain magnetic field vector in generation of the indoor magnetic field map, wherein the decision is based on the validity determination.

11. The apparatus of claim 10 , wherein the apparatus is further caused to: rank users, each user being associated with at least one measuring device used in measurement of magnetic field vector, on the basis of at least one of the following: validity determination of the acquired magnetic field vectors, utilization rate of data acquired from a specific user, amount of collected data by a specific user, amount of references to social network services from a specific area where measurements have been done by a specific user, amount of advertisements associated to a specific area where measurements have been done by a specific user, amount of revenue associated to a specific area where measurements have been done by a specific user.

12. The apparatus of claim 5 , wherein the apparatus is further caused to: acquire at least one indoor magnetic field map update with respect to at least one of the magnetic field vector and the uncertainty measure in at least one location from a positioning device that is to be located in the building, wherein the positioning device is configured to transmit information regarding at least measured magnetic field vector.

13. The apparatus of claim 5 , wherein the apparatus is further caused to: acquire information related to magnetic field vector measurements from a plurality of measuring devices, wherein the magnetic field vector measurements correspond to at least one location where the measurement paths of the measuring devices have overlapped; estimate a true magnetic field reference vector from the acquired magnetic field vector measurements based on at least one predetermined criterion; compare acquired non-reference magnetic field vector measurements at the location of the overlap to the true magnetic field reference vector; determine calibration for the non-reference magnetic field vector measurements at least partly on the basis of the comparison result; and apply the determined calibration to all magnetic field measurements acquired from measurement devices corresponding to the non-reference magnetic field vector measurements in order to acquire commensurable and usable magnetic field measurements for the indoor magnetic field map generation from each of the plurality of measuring devices.

14. The apparatus of claim 1 , wherein the apparatus is further caused to: upon determining that a measuring device is at a predetermined location where a true magnetic field vector is known, cause at least one of the following to take place: a calibration process of at least the measured magnetic field vector of the measuring device, wherein the calibration process applies a scaling parameter and/or bias vector determined from the difference between the measured and true magnetic field magnitudes, connection establishment between a data base entity and the measuring device in order to actuate a software for magnetic field vector measurements and/or to enable the communication of the measured at least one magnetic field vector from the measuring device to the data base entity.

15. A method, comprising: acquiring information indicating a magnetic field vector and information relating to an uncertainty measure of the magnetic field vector in at least one known location inside a building, wherein the indicated magnetic field vector represents measured magnitude and direction of the earth's magnetic field affected by the local structures of the building, and wherein the known location is defined in a frame of reference of a floor plan of the building, and the uncertainty measure represents at least one of uncertainty of the magnitude of the magnetic field vector and uncertainty of the direction of the magnetic field vector and indicates location-specific reliability of the measured magnetic field vector in the at least one known location; generating the indoor magnetic field map for the building on the basis of at least the acquired information and the floor plan, wherein the indoor magnetic field map comprises the magnetic field vector and the uncertainty measure of the magnetic field vector for the at least one location inside the building; and applying the uncertainty measure of the magnetic field vector comprised in the indoor magnetic field map for at least one of the following: location estimation of a person in the building ( 100 ), updating the generated indoor magnetic field map with new magnetic field vector measurements.

16. A system, comprising: a magnetic field measuring device configured to: measure a magnetic field vector in at least one known location inside a building, wherein the magnetic field vector represents measured magnitude and direction of the earth's magnetic field affected by the local structures of the building and wherein the at least one known location is defined in a frame of reference of a floor plan of the building; and transmit the measured magnetic field vector to a data base located in a network over a wireless communication link, wherein the system further comprises the data base processor having access to a floor plan of at least part of the building, the data base processor being configured to: receive information indicating the magnetic field vector from the magnetic field measuring device over the wireless link; determine an uncertainty measure of the magnetic field vector, wherein the uncertainty measure represents at least one of uncertainty of the magnitude of the magnetic field vector and uncertainty of the direction of the magnetic field vector and indicates location-specific reliability of the measured magnetic field vector in the at least one known location; generate the indoor magnetic field map for the building on the basis of at least the acquired information and the floor plan, wherein the indoor magnetic field map comprises the magnetic field vector and the uncertainty measure of the magnetic field vector for the at least one location inside the building; apply the uncertainty measure of the magnetic field vector comprised in the indoor magnetic field map for at least one of the following: location estimation of a person in the building, updating the generated indoor magnetic field map with new magnetic field vector measurements; and provide, on request, at least part of the generated indoor magnetic field map to a positioning device that is to determine its location inside the building.

17. The system of claim 16 , the system further comprising a first radio frequency identification unit configured to: determine that the magnetic field measuring device, comprising a second radio frequency identification unit, is coupled to the first radio frequency identification unit, wherein a true magnetic field magnitude at the location of the first radio frequency identification unit is known; and cause at least one of the following to take place: a calibration process of at least the measured magnetic field magnitude and/or bias of the magnetic field measuring device, wherein the calibration process applies a scaling parameter and/or bias vector determined from the difference between the measured and true magnetic field magnitudes, connection establishment between a data base processor and the magnetic field measuring device in order to actuate a software for magnetic field vector measurements and/or to enable the communication of the measured at least one magnetic field vector from the magnetic field measuring device to the data base processor.